In Yuru Yuri at the start it is presumed that Akari is a 6th grader, and her friends Kyouko and Funami are 7th graders as they are a grade ahead of Akari.
They have gone to 2 comic-con, school trips, and summer vacations. Therefore, if Kyouko and Funami are in grade 7 for the first comic-con trip, and are in grade 7 going to grade 8 in their summer vacation, that would imply that they were in 8th grade during their second comic con visit and going from grade 8 to 9 in their second summer vacation. Therefore, they should no longer be enrolled in school after their second summer vacation, because therefore they would have graduated middle school and be enrolled in high school.